The invention relates to a marine fuel system for a two cycle fuel injected engine, and more particularly to a system for removing and recirculating fuel puddles including heavy fuel ends from low points in the crankcase, and preventing high return air flow rates at high engine speed otherwise causing fuel foaming.
In two cycle internal combustion engines, at idle speed, heavy fuel ends condense on the walls of the crankcase and accumulate in the lowest part of the crankcase, i.e. form fuel puddles. Various systems are known for recirculating the puddled fuel back into the crankcase for subsequent combustion. For example, the puddled fuel in the crankcase of one of the cyclinders is pumped out during the combustion power stroke of the piston in that cylinder pressurizing that section of the crankcase, and the puddled fuel is supplied to the crankcase of another cylinder whose piston is in its charging stroke thus creating a vacuum drawing fuel into that section of the crankcase. In other systems, the puddled fuel is recirculated with the fresh incoming fuel.
In fuel injected engines, it is important to accurately control the quantity of fuel delivered to the engine through the fuel injectors. It is common to use a high pressure pump to supply fuel to the injectors, with a pressure regulator providing an essentially constant fuel pressure at the injector. Excess fuel, i.e. the amount over and above that required by the engine, is recirculated, usually through a vapor separator, back to the fuel pump.
It is known in the prior art to provide a puddled fuel return line from the crankcase to the vapor separator, where the excess puddled fuel is mixed with the incoming fuel and re-routed to the fuel injectors. A shortcoming of such system is that at high engine speed, substantially all the fluid passing through the puddled fuel return line from the crankcase is gaseous (air), and because of its high flow rate, it tends to cause foaming of the fuel in the vapor separator. This foamed fuel passes through the vapor vent line to the induction system, causing an over-rich condition.
In the present invention, a shut-off valve is provided in the puddled fuel return line from the crankcase. At low engine speed, the valve is open, allowing fluid flow from the crankcase to the vapor separator. At high engine speed, the valve is closed, stopping the otherwise gaseous flow. With no flow from the crankcase to the vapor separator through the puddled fuel return line, the fuel in the vapor separator remains liquid, allowing proper engine operation at high speed.